The present invention relates to a hologram transfer film with good hologram transferability which can easily apply a hologram to various objects.
The present invention also relates to a production process of a hologram transfer film suitable for small lot production of a plurality of kinds of products with high efficiency.
The present invention further relates to a photocurable resin composition and a hologram and a forgery-preventing sheet using the photocurable resin composition, and more particularly to a photocurable resin composition, which can yield a coating having simultaneously heat resistance, softness and other properties, and a hologram and a forgery-preventive sheet, with the hologram being infused therein as a lustrous thread, using the resin composition.
In conventional hologram transfer films, in general, a surface relief hologram layer, wherein a hologram is formed by providing concaves and covexes on the surface thereof, is mainly used in a hologram-forming layer. A representative construction of the hologram transfer film known in the art comprises a substrate film having thereon a release layer, a surface relief hologram layer, a reflective thin film layer, and a heat-sensitive adhesive layer.
At the time of thermal transfer, in other words, hot stamping, the hologram layer in the hologram transfer film should be sharply cut and transferred onto an object, that is, should have good transferability and should be exactly transferred onto an object.
Many of the conventional hologram transfer films, however, have unsatisfactory hologram transferability, and are very unstable in transfer process. That is, the hologram layer can be in some cases satisfactorily transferred and in some cases cannot be satisfactorily transferred. Therefore, an improvement in the transferability has been desired in the art.
Accordingly, it is a first object of the present invention to provide a hologram transfer film which can solve the above problem of the prior art and enables a hologram to be easily and exactly transferred with good stability in the transfer process.
An example of a conventional forgery-preventive sheet is such that a forgery-preventive printed pattern (a ground design) is formed by printing fine dots or hairlines on the surface of the sheet. In this sheet, upon copying in a light mode, the dots or the lines cannot be clearly copied, while upon copying in a deep mode, the dots are blurred and seen like lines or letters, and the lines are blurred to thicken the lines. In recent years, however, this method has become insufficient for preventing forgery.
In order to solve this problem, a forgery-preventive sheet has been proposed wherein, for example, a lustrous thread is infused into one side of a base sheet (Japanese Patent Laid-Open No. 56377/1995). This forgery-preventive sheet is intended to prevent forgery by utilizing a phenomenon such that, even upon color copying, a metallic color does not appear in portions corresponding to the lustrous thread.
Further, diffraction gratings or relief holograms have hitherto been used for the decoration or the prevention of forgery of various cards, securities and the like.
With expansion of the above applications, the diffraction grating or the relief hologram has become required to have such properties as the capability of being infused as watermarks into papers, excellent strength, heat resistance, scratch resistance, water resistance, chemical resistance, and adhesion to substrates, and conformability to flexing or expansion/contraction of objects with holograms or diffraction gratings being applied thereon. In particular, in the case of diffraction gratings or relief holograms formed of a cured product of a conventional photocurable coating composition, a resin used in the production thereof loses flexibility upon photocuring, and, thus, flexing or expansion/contraction of an object with the holograms or the diffraction grating being applied thereon results in loss of the function of the diffraction grating or the relief hologram.
Accordingly, it is a second object of the invention to provide a photocurable resin composition that can form a diffraction grating, a hologram or the like which can solve the problems of the prior art and has excellent strength, heat resistance, scratch resistance, water resistance, chemical resistance, and adhesion to substrates, and conformability to flexing or expansion/contraction of objects with holograms or diffraction gratings being applied thereon, and to provide a hologram or diffraction grating sheet.
According to the first invention, there is provided a hologram transfer film comprising: a substrate film; a transfer layer provided on the substrate film, the transfer layer comprising a hologram-forming layer and a heat-sensitive adhesive layer provided in that order on the substrate film, the hologram-forming layer having a breaking strain of 0.5 to 15% at 25xc2x0 C. and a breaking strain of 0.5 to 30% at 120xc2x0 C. The present inventor has found that the transferability is influenced by strain at break of the hologram-forming layer, which had led to the completion of the present invention.
A process for producing the hologram transfer film according to the first invention comprises the steps of: providing a film having a hologram-forming layer and a film having a heat-sensitive adhesive layer in respective independent steps; and then laminating these films in combination according to applications of the hologram to prepare the hologram transfer film. According to this production process, mere lamination of a film having a hologram-forming layer and a film having a heat-sensitive adhesive layer, which have already been produced in respective independent steps, in combination according to need can provide a hologram transfer film. Therefore, this production process is particularly suitable for small lot production of a plurality of kinds of products.
In order to attain the second object, the present inventor has made further studies on material systems proposed by the present applicant in Japanese Patent Laid-Open No. 156273/1986 and Japanese Patent Publication No. 54502/1993, and, as result, has found that this object can be attained by regulating the Young""s modulus at 1% elongation of cured products of photocurable resin compositions using these materials to a specific range. This had led to the completion of the second invention.
Thus, according to the second invention, there are provided a photocurable resin composition for providing a formative layer formed of a hologram or a diffraction grating on a substrate having a Young""s modulus at 1% elongation of not less than 2,000 MPa at 25xc2x0 C. and a Young""s modulus at 1% elongation of not less than 350 MPa at 120xc2x0 C., wherein the photocurable resin composition provides a cured product of which the Young""s modulus at 1% elongation at 25xc2x0 C. and the Young""s modulus at 1% elongation at 120xc2x0 C. are respectively lower than those of the substrate, and a hologram or diffraction grating sheet comprising: a substrate film; a formative layer formed of a hologram or a diffraction grating provided on the substrate film; and a pressure-sensitive adhesive layer provided on the formative layer, the formative layer having Young""s modulus at 1% elongation at 25xc2x0 C. and the Young""s modulus at 1% elongation at 120xc2x0 C. respectively lower than those of the substrate.